Various immunosuppressants such as cyclosporin and FK506 have been developed for controlling biological immunoreactions in collagen diseases, autoimmune diseases and rejection for organ transplantation. However, since such immunosuppressants are reactive to cells other than immunocompetent cells, side effects of these agent should be taken into consideration.
Various methods have been investigated for using antibodies that specifically react with target cells. For example, the target cell with which the antibody has reacted is expected to be lysed by reacting with a complement. While there are species-specific complement control membrane factors (such as DAF, decay accelerating factor; MCP, membrane cofactor protein; and HRF20, 20 kDa homologous restriction factor) on human cell membranes, they can induce no cytolysis reaction via complement reactions for preventing reactions among homologous human complements.
On the other hand, it was found that IgM antibodies in human serum that react with the HIV-infected cells are able to yield the cytolysis reaction of the HIV-infected cells via the human complement by overcoming the complement control membrane factors. It was revealed that the IgM antibody can exhibit such action as described above against gangliosides such as GM2 and Gg4 whose expression is enhanced by HIV-infection (Japanese Patent Application Laid-Open No. 9-227409).
L55 has been reported as the human IgM monoclonal antibody against GM2 of the gangliosides, wherein L55 is produced by immortalizing human B lymphoblast strain with EB virus. The HIV-infected cells after treating with this human IgM monoclonal antibody have been found to yield cytolysis via a reaction with the human complement.